SanDisk Extreme Pro USB 3.1 Solid State Flash Drive

Stated speed from SanDisk's website:
Read: up to 420MB/s
Write: 380MB/s

My results:

Blackmagic Disk Speed Test

NTFS Format (using Paragon)
Read: 380MB/s
Write: 340MB/s

Mac OS Extended Format
Read: 380MB/s
Write: 330MB/s

Real world transferring between a Crucial MX300 SSD (Mac OS Extended)
Read: ~350MB/s
Write: ~350MB/s

Slightest idea why the write speed when formatted to the native Mac OS Extended was slower than NTFS using Paragon 16, but it constantly was.